1. Technical Field
The present invention relates to a boom extending and retracting apparatus that extends and retracts a telescopic boom of a crane.
2. Related Art
A crane is equipped with a telescopic boom to lift goods. There has been known a telescopic boom in which a plurality of boom members are provided as to be slid with respect to each other and one telescopic cylinder is provided to slide the plurality of boom members one by one to extend. However, when the plurality of boom members are slid one by one with one telescopic cylinder, it may take time to extend or retract the telescopic boom. Therefore, in a crane disclosed in Patent Literature 1, a differential fluid circuit as well as a normal fluid circuit is provided for a fluid circuit to inject fluid such as hydraulic oil into the telescopic cylinder. By extending the telescopic cylinder with the action of the differential fluid circuit, it is possible to increase the extension speed of the telescopic cylinder. Therefore, it is possible to shorten the extension time of the telescopic boom, and possible to improve the convenience.    Patent Literature 1: Japanese Patent No. 4040856
However, in Patent literature 1, an additional switch is used to change and select an activated one between the differential fluid circuit and the normal fluid circuit. In this case, in the course of the work, the operator of the crane always has to know and identify the selected and using circuit from the differential fluid circuit and the normal fluid circuit, while executing a complex crane operation of the telescopic boom. And, the operator has to flip the additional switch during the work repeatedly, in accordance with and based on the emphasizing usage state. Therefore, management items during the work are increased, and consequently the burden on the operator increases.
Thus, in a crane, both to reduce the burden on the operator and to improve the convenience of the telescopic boom are required to be realized.
The boom extending and retracting apparatus according to the present invention includes: a telescopic boom including a plurality of boom members that can slide with respect to each other; a telescopic cylinder configured to extend and retract the telescopic boom by sliding the plurality of boom members, the telescopic cylinder including: a cylinder tube having an internal space filled with fluid; and a piston rod having piston dividing the internal space of the cylinder tube into an extension-side oil chamber and a retraction-side oil chamber, the piston rod moving along an inner surface of the cylinder tube to extend and retract the telescopic cylinder; a fluid circuit including a normal fluid circuit and a differential fluid circuit, the normal fluid circuit injecting fluid only into the extension-side oil chamber of the telescopic cylinder, and the differential fluid circuit injecting the fluid into the extension-side oil chamber while the fluid in the retraction-side oil chamber can be moved to the extension-side oil chamber; a controller configured to choose one of the normal fluid circuit and the differential fluid circuit, in order to extend and retract the telescopic boom; and an operating lever turned from a neutral position in order to extend the telescopic boom, wherein after the operating lever is turned to an extension side and the controller starts extending the telescopic boom using the differential fluid circuit, when the operating lever is turned to the extension side again via the neutral position, the controller chooses the normal fluid circuit to extend the telescopic boom using the normal fluid circuit.
Preferably, the boom extending and retracting apparatus of the crane further including a detection member configured to detect an extension amount of the telescopic cylinder, wherein, in a case where the controller determined an interruption of the extension of the telescopic boom based on the detected extension amount by the detection member before the operating lever is turned back to the neutral position, the controller chooses the normal fluid circuit to extend the telescopic boom using the normal fluid circuit.
Preferably, the boom extending and retracting apparatus of the crane further including a timer configured to measure a repeated operation time that has counted from a turned back timing of the operating lever to the neutral position until the repeated operation of the operating lever to the extension side, wherein: when the repeated operation time is shorter than a predetermined period of time, the controller chooses the normal fluid circuit based on the repeated operation of the operating lever to the extension side, and changes the extension of the telescopic boom with using the normal fluid circuit; and when the repeated operation time is equal to or longer than the predetermined period of time, the controller chooses the differential fluid circuit based on the repeated operation of the operating lever to the extension side, and continues the extension of the telescopic boom with using the differential fluid circuit.
Preferably, the boom extending and retracting apparatus of the crane further including a switch configured to set an availability or unavailability of the differential fluid circuit, wherein, when the operating lever is repeatedly operated to the extension side, the controller chooses the normal fluid circuit regardless of the setting of the switch, and changes the extension of the telescopic boom with using the normal fluid circuit.
Preferably, the boom extending and retracting apparatus of the crane further including a display member configured to display the activated function of the fluid circuit between the normal fluid circuit and the differential fluid circuit.
With the present invention, when the operating lever was operated from the neutral position in the extension side as for the telescopic boom to be started to be extended with using the differential fluid circuit and then the operating lever is again operated in the extension side, the control part selects the normal fluid circuit mode. That is, the activating mode of the fluid circuit is switched from the differential fluid circuit to the normal fluid circuit. The operator can switch the activating mode of the fluid circuit just by turning the operating lever repeatedly in the extension side. Therefore, with the present invention, it is possible to achieve an improved convenience in which the normal fluid circuit and the differential fluid circuit can be used switchably to extend the telescopic boom. In addition, it is possible to realize the intuitively knowable handleability in which the operating lever is only and repeatedly operated in the extension side, and therefore to reduce the burden of the operator. Moreover, there is no need to provide any additional switch to flip the fluid circuit during the work, and therefore it is possible to reduce the cost for the switch and also to save the space for installing the switch.